Till now there has been not many sound MODs for Lollipop Z2. But you can give a shot at this http://forum.xda-developers.com/showthread.php?t=3067061.
If it helps, gr8! oter den that, you have to wait for the devs to come out with LP mods as I be...
5.1.1 is fine as you can root it. Just install Recovery( nuts dual recovery/ choose your version carefully & Follow instructions). if you'r going to upgrade to 6.0.1, i would suggest this kernel -http://forum.xda-developers.com/showthread.php?t=29...
XZdual recovery currently doesbnot support MM. Dont use it!! Search for compatible MM recovery. Its available. But ya, you have to flash new ftf for now to solve your current problem.
"Xcites: Develop: Achieve"
1. reboot to recovery of ur choice(on reboot,green light appears with vibration,press either Vol+/Vol- (vol+=cwm;vol-=twrp)to boot to recovry while green light is on) and there wil b option for backup. Backup all by checkmarking(compression cn b i...
everything fine till now. been using for a month now. just to be cautious, do a backup b4 flashing.
Results may vary 4m ROM to ROM but it shud be fine. And if ur on stock based ROM, shud be fine.
Just give it a shot buddy!
Sent from my D6503